Not only do you have the wrong thread, I think you have the wrong forum.
How this has anything to do with a spudgun, I don't know. If you're planning on shooting these things, you're in violation of the <a href="http://localhost/forums/viewtopic.php?t=11450">forum rules</a> (3.C.i). (I'm getting tired of referring to that page today. Doesn't anyone read it?)
For the moment, I'll give you the benefit of the doubt.
When a quantity is given in mass, you need a balance or a scale. There is no measuring cup that equals 20 grams at all times. One cup of lead would weigh more than one cup of water. Without knowing the density of what you want to measure, I can't tell you what volume you need to measure out.
Beyond that, you could easily answer the "how many teaspoons in a cup" question with a quick <a href="http://www.google.com/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial_s&hl=en&q=how+many+teaspoons+in+a+cup&btnG=Google+Search">Google search</a>.
I mean no offense by this, but if you can't figure this out on your own, you shouldn't be playing with pyrotechnics.